The present invention relates to a liquid crystal light valve (LCLV) used for a large-screen image projection apparatus and optical data processing apparatus and manufacturing method thereof, and more particularly to an LCLV with an improved layer structure having a reflecting layer.
Using the electro-optical characteristic of liquid crystal whose dynamic characteristic changes according to the presence or absence or the amount of incident writing light, an LCLV modulates projection light with the liquid crystal and is used to provide amplification light and to form an image and in the changing of its wavelength of the applied light. Such an LCLV is used for light reflection and transmission projection systems and optical data processors. Recently, the study of its application to household equipment has been proceeding.
FIG. 1 illustrates a conventional LCLV. In FIG. 1, transparent electrodes 3 and 3a to which a driving voltage is applied adhere to the inner surface of two parallel transparent substrates 2 and 2a. Liquid crystal LQ between transparent substrates 2 and 2a keep a certain distance between spacers 8 and 8a is in contact with orientation layers 7 and 7a. A sandwich layer composed of a photoconductor 4, a light interceptor 5 and a reflecting layer 6 is placed between electrode 3 of transparent substrate 2 which is on the side of incident writing light 9a, and the opposing orientation layer 7. In FIG. 1, reference numeral 1 denotes a filter while 9b denotes projection light.
In operation of the LCLV, a control voltage for dynamically controlling the liquid crystal which double-refracts projection light 9b forming an actual image must be switched by photoconductor 4 activated by writing light 9a having an image signal. Therefore, an LCLV should be designed so that when no writing light is incident, the impedance of a photoconductor is far greater than that of liquid crystal and when writing light is incident, the impedance of the photoconductor is far less than that of liquid crystal. However, the elements of the layer structure are physically joined, meaning that a deviation of the junction characteristic (for example, electrical contact resistance, that is, impedance) actually exists at each junction portion. Particularly, the junction characteristic of the elements of the layer structure is disadvantageous if each layer is thick. Since reflecting layer 6 is a multilayer consisting of dielectrics having high or low refractive indexes, it greatly affects the deterioration of the overall junction characteristic. Such a reflecting layer is usually stacked with more than ten layers of material made of SiO.sub.2 and TiO.sub.2 or MgF.sub.2 and ZnS and has a high reflectance of about 95%. However, since the wavelength region in which complete reflection takes place is only plus or minus tens of nanometers from a specific reference wavelength according to the difference in reflectances of the two materials, complete reflection throughout the whole visible light spectrum can not be expected. To solve such a problem, the reflecting layer should be a stack of dielectrics having various reference wavelengths, eventually increasing the overall thickness of the layer. The increased thickness of layer results in raising the stress on the reflecting layer so that the junction characteristic of an adjacent layer, for example, the photoconductor or light intercepting layer, becomes poor, which in turn lowers product reliability and increases production costs.
As an improvement to the problem, an LCLV having an additional junction layer was disclosed in U.S. Pat. No. 4,799,773 which usually uses SiO.sub.2 or CdTe as the junction layer. However, such an LCLV has a thicker photoconductor (over 30.mu.m or so) for an impedance matching, which results in increase in production cost and reduction in productivity. In addition, since the reflecting portion of the reflecting layer is narrow, a filter (as an additional improvement) is required to be adhered to a light source.